1. Field of the Invention
The present invention relates generally to fasteners and more particularly to fasteners and fastening methods for joining panels of dissimilar materials to a fixed base.
The necessity to achieve optimal fuel economy in the production of automotive vehicles results in increased emphasis on ultralight vehicle construction. One promising lightweight body construction concept results in the use of lightweight metallic space frames, such as those formed from aluminum which serve as a skeleton to which lightweight external skins are attached as closure panels. This construction technique offers significant weight reduction potential, but it also brings problems which must be solved relating to the problems associated with joining the panels, which are often formed of plastic or other material having a higher coefficient of thermal expansion than the space frame, to the skeleton or space frame.
Because of the fact that space frames have rigid jointed geometry, they are difficult to build in close tolerances in three-dimensional space. As a result of this, means must be provided on the assembly line for a vehicle to align all external and internal surfaces and other closures in a way to produce acceptable body fits, margins about the plan view projection of the body panels and the flushness of adjacent panels. In current production technology, the desired flushness and other fits are achieved through methods such as those shown in U.S. Pat. No. 4,529,244 and U.S. Pat. No. 4,597,153 to Zaydel. Certain improvements in this technology have been disclosed in U.S. Pat. No. 4,868,968 and U.S. Pat. No. 4,912,826 assigned to the assignee of the present invention. These approaches, however, require significant investment in tooling and fixturing to achieve the desired body fit, making the approach impractical in all but the highest production vehicles.
One of the problems sought to be solved in the aforementioned production techniques is that of compensating for differences in coefficients of thermal expansion between adjacent panels, i.e., the underlying space frame and the plastic skin or decorative body panel which is laid over it. Means must be provided to allow certain movement between the space frame and the adjacent body panel to accommodate thermal induced growth and shrinkage.
While certain freedom of movement between adjacent panels is provided in the fasteners of the previously mentioned prior art, the automotive body art does not teach a method of joining decorative body panels to a space frame in a fashion which permits adjustable positioning, both with respect to movement for and away from the planar surface of the underlying subframe and parallel to the facing surface of such frame.